Clamping device for a cutting insert

ABSTRACT

An insert clamp secures a cutting insert having a central hole to a tool holder. The clamp includes a forward protrusion to be received in the central hole of the insert, a central body portion provided with a pressing part to press down the upper surface of the insert and a screw hole for a clamping screw to pass through, and a rear protrusion having a rear contact surface to come in contact with a rearward slanting surface of the tool holder. The forward protrusion is formed on the forward end of the insert clamp, an inside surface of the forward protrusion extends downward in a spaced state apart from the inner wall of the central hole of the insert, and a distal portion of the inside surface the forward protrusion is provided with a protuberance of convex curved surface to come in tangential contact with the inner wall of the insert. The pressing part is formed on the bottom surface of the central body portion of the insert clamp, and has convex curved surfaces to come in tangential contact with the upper surface of the insert on both regions of the bottom surface of the central body portion which is bisected by a central line passing through the forward protrusion and the screw hole.

TECHNICAL FIELD

The present invention relates to a device clamping a cutting insert to atool holder. A tool holder of this kind is particularly useful for anindexable insert with a central hole to be secured in a mounting seat ofthe tool holder.

BACKGROUND ART

An indexable inserts is mounted on a cutting tool holder for machining aworkpiece and may take various shapes such as square and triangle withan equal corner angle all around the insert, or rhombic or rhomboidicshapes with acute nose point angles.

In general, a machining tool mounted with this indexable insert is usedfor drilling, milling, and turning. In these various machining methods,the cutting insert is secured onto the seat of the tool holder by aclamping means and provides a cutting edge to contact the workpiece.

A clamping means to secure an insert with a central hole to a toolholder has been disclosed in EP 0759826 B1. This clamping means intendsto keep the insert in place in the pocket so that the clamping force isacting on both the top surface and in the central hole wall of theinsert without any tendency of coming apart from its underneathsupporting surface of the seat of the tool holder. And the rear endportion of this clamp is adapted to come into abutment with an inclinedrear surface provided on the holder body.

However, this clamp is characterized by a point contact between the holewall of the insert and the front clamp projection at a point distantlyprovided from the top surface of the insert by means of arranging aforward protrusion having an axis of symmetry that is oriented at aninclined angle(β) relative to the axis of the hole. In this clampingstructure, the contact point pressing the hole wall has only aninfinitesimal area. Accordingly, when the cutting tool is used for aprolonged period of time, the contact point is susceptible to wearingand the clamp is got loosened. Hence, there has been a concern that theclamping becomes too loose for an appropriate cutting operation if theclamp is not tightened further once in a while.

Also, with the above insert, the flat underneath surface is notguaranteed to achieve a flat surface abutment against the top surface ofthe insert. In other words, as the contact position of the end surfaceof the rear protrusion on the inclined contact surface is varieddepending on the manufacturing variations of inserts or clamps, thecontact between the flat underneath surface and the top surface of theinsert may not be an actual planar contact, but may result in a pointcontact at a forward border position “A” or a rearward border position“B” of the flat surface as illustrated in FIG. 6. If this is the case,the contact point is also susceptible for wearing and the clamping getsloosened under a prolonged use of the tool. Especially, when the contactis made at a forward border position “A”, a force lifting the rearportion of the insert apart from the bottom face of the insert pocketdue to a shear force applied on the insert nose is not effectivelycounteracted, and an ultimate insert failure may result. Also, sinceshear force is mainly applied on one active edge of the two edgesadjacent to the nose, there is a tendency of lifting a portion of theinsert opposite to the active edge apart from the bottom face of theinsert pocket. However, the aforesaid clamp is inefficient forsuppressing this tendency, and this becomes more problematical if theinsert is in triangular shape where there is only one upstanding supportsurface of the insert pocket.

On the other hand, in Korean registered patent no. 0450439, the inventorproposed a contact structure, in which a contact portion formed on theinner side of the forward protrusion has a surface contact over acertain length with the inner wall of the central hole of an insert sothat wearing is reduced. Also, pressing portions of flat surface areprovided on both flanks of the forward protrusion to press down theinsert.

However, in this structure, as the end surface of the rear protrusion isdisplaced on the inclined contact surface, a smooth surface contact isnot achieved between the contact portion and the inner wall of thecentral hole but a point contact may occur at a top position “C” or abottom position “D” as illustrated in FIG. 7. In this case, the contactpoint is also susceptible for wearing and the clamping gets loosenedunder a prolonged use of the tool. Especially, when the contact is madeat a top position “D” the contact point is so close to the upper surfaceof the insert that the support point for transverse clamping forcebecomes unstable. Also, since pressing points are made around flank rimof the central hole, the force to counteract a force lifting the rearportion of the insert apart from the bottom face of the insert pocketdue to a shear force applied on the insert nose is not sufficient andinsert failure may occur ultimately.

SUMMARY OF THE INVENTION

The present invention has been conceived to solve the aforementionedproblems of clamping failure due to contact point wearing and a severedisplacement of contact points in the prior art, and accordingly anobject of the present invention is to provide an insert clamp with asimple structure to clamp a cutting insert to a tool holder securely andstably.

According to the present invention, there is provided an insert clampfor securing a cutting insert to a tool holder, the cutting inserthaving a central hole with its axis perpendicular to an upper surface,comprising: a forward protrusion to be received in the central hole ofthe insert, a central body portion provided with a pressing part topress down the upper surface of the insert and a screw hole for aclamping screw to pass through, and a rear protrusion having a rearcontact surface to come in contact with a rearward slanting surface ofthe tool holder; wherein the forward protrusion is formed on the forwardend of the insert clamp, an inside surface of the forward protrusionextends downward in a spaced state apart from the inner wall of thecentral hole of the insert, and a distal portion of the inside surfacethe forward protrusion is provided with a protuberance of convex curvedsurface to come in tangential contact with the inner wall of the insert;and the pressing part is formed on the bottom surface of the centralbody portion of the insert clamp, and has convex curved surfaces to comein tangential contact with the upper surface of the insert on bothregions of the bottom surface of the central body portion which isbisected by a central line passing through the forward protrusion andthe screw hole.

According to a feature of the present invention, the pressing part is apair of protuberances in hemispherical shape separated by a lengthspanning across the central line inside the upper surface area of theinsert.

According to a feature of the present invention, a line joining the pairof protuberances is perpendicular to the central line and is separatedrearward from the forward protrusion.

According to another feature of the present invention, the pressing partis a protuberance in an elongated hemi-cylindrical shape extendingacross the central line with a length spanning inside the upper surfacearea of the insert.

According to another feature of the present invention, the protuberanceextends in a direction perpendicular to the central line and isseparated rearward from the forward protrusion.

According to still another feature of the present invention, the rearcontact surface of the rear protrusion is convex curved in thetransection cutting through the contact surface as well as in thevertical section passing through the central line.

According to still another feature of the present invention, an outsidedistal portion of the forward protrusion is chamfered or rounded.

The insert clamp according to the present invention has the followingtechnical effects.

The insert clamp according to the present invention has an effect toprevent wearing at the contact point and provide a durable clamping.Also, the insert clamp of the present invention has an effect that asmooth surface contact between the forward protrusion and inner wall ofthe insert hole is guaranteed, while the point of action for thetransverse clamping force is stably fixed at the middle height of theinsert hole. This structure also allows a clearance between an upper rimof the insert hole and a corner of the clamp bottom face so that theclamp and the insert can achieve a snug coupling.

In the present invention, a ‘smooth surface contact’ is contrasted witha ‘point contact’ in prior art and here is defined as a surface contactwhere tangential contact is achieved between two curved surfaces orbetween a curved surface and a flat surface so that resistance towearing is enhanced over the point contact.

The clamp of the present invention has an effect to prevent pointcontacts with displaced contact position so that a smooth surfacecontact is guaranteed at a fixed position. Especially, an effectivecounterforce is provided against the force lifting the rear portion ofthe insert apart from the bottom face of the insert pocket due to ashear force applied on the insert nose. Also, although shear force ismainly applied on one active edge of the two edges adjacent to the nose,an effective counterforce is provided against the tendency of lifting aportion of the insert opposite to the active edge apart from the bottomface of the insert pocket. This effect becomes more pronounced if theinsert is in triangular shape for which there is only one upstandingsupport surface in the insert pocket.

In the insert clamp according to the present invention, the rear contactsurface and the two protuberances on the bottom face constitute a strongand stable support structure, so-called ‘triangular support structure.’Especially, this ‘triangular support structure’ provides an effect toguarantee a stable and durable clamping state even for cases where twocorresponding contact portions are not symmetric and the two contactportions are rather imbalanced in their heights.

Since this ‘triangular support structure’ is also constituted among theprotuberance of the forward protrusion and the two protuberances on thebottom face, the insert clamp in accordance with the present inventionhas an effect to provide a durable and stable clamping structure with nomobility over the entire body of the insert clamp.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view depicting a tool holder assembly using aninsert clamp in accordance with the present invention.

FIGS. 2 to 5 are plane or perspective views illustrating embodiments ofthe insert clamps in accordance with the present invention.

FIGS. 6 and 7 are sectional views depicting related prior art.

DETAILED DESCRIPTION

FIG. 1 is a sectional view depicting a tool holder assembly using aninsert clamp in accordance with the present invention. And FIGS. 2 to 5illustrate embodiments of the insert clamps in accordance with thepresent invention in plane or perspective views.

As shown in FIG. 1, the insert clamp 20 of the present invention is usedto secure a cutting insert 10, which has a central hole 12 with its axisperpendicular to an upper surface 11, to a tool holder 40. The cuttinginsert 10 may be seated on a shim 13 in the tool holder's insertreceiving pocket 42. The insert clamp 20 comprises a forward protrusion21 to be received in the central hole 12 of the insert 10, a centralbody portion provided with a pressing part 22 to press down the uppersurface 11 of the insert 10 and a screw hole 23 for a clamping screw 30to pass through, and a rear protrusion 24 having a rear contact surface25 to come in contact with a rearward slanting surface 41 of the toolholder 40.

The forward protrusion 21 is formed on the forward end of the insertclamp 20, an inside surface 21 a of the forward protrusion extendsdownward in a spaced state apart from the inner wall 12 a of the centralhole of the insert, and a distal portion of the inside surface of theforward protrusion is provided with a protuberance 21 b of convex curvedsurface to come in tangential contact with the inner wall of the insert.

Here, the forward protrusion 21 is preferably formed substantially in acylindrical shape extending downward with a diameter less than the innerdiameter of the central hole of the insert. The extended length of theforward protrusion 21 is preferably determined such that theprotuberance 21 b is positioned approximately at the middle height ofthe central hole 12. This will lead an appropriate positioning of thepoint of action for the transverse clamping force against the insert.The radius of curvature of the convex curve of the protuberance 21 b ispreferably made large enough to enable a smooth surface contact to theinner wall 12 a of the central hole of the insert.

The inside surface 21 a of the forward protrusion, except over theportion of the protuberance 21 b, is preferably formed substantially inparallel with the inner wall 12 a of the central hole of the insert. Onthe other hand, the outside surface of the forward protrusion is notnecessarily in parallel with the inner wall 12 a of the central hole ofthe insert. The outside surface is preferably rounded as shown in FIG.1, or the outer portion of the bottom end surface of the forwardprotrusion 21 is machined to be sloped as shown in FIGS. 2 to 5. Theseare provided to easily introduce the forward protrusion 21 into thecentral hole of the insert. In the present invention, the above shapesof the forward protrusion 21 for easy introduction to the central holeare understood as a sort of the chamfering of the outer bottom end 21 dof the forward protrusion 21. Anyhow, the foremost end 21 e of theforward protrusion 21 is preferably not protruded ahead before thecentral hole of the insert.

The pressing part 22 in accordance with the present invention is formedon the bottom surface of the central body portion of the insert clamp,and has convex curved surfaces to come in tangential contact with theupper surface of the insert on both regions of the bottom surface of thecentral body portion which is bisected by a central line passing throughthe forward protrusion 21 and the screw hole 23.

One embodiment of the pressing part 22, as shown in FIG. 2, is a pair ofprotuberances 22 a in hemispherical shape separated by a length spanningacross the central line L inside the upper surface area of the insert.The line joining the pair of protuberances 22 a is preferablyperpendicular to the central line and is separated rearward from theforward protrusion 21.

Another embodiment of the pressing part 22, as shown in FIG. 3, is aprotuberance 22 b in an elongated hemi-cylindrical shape extendingacross the central line with a length spanning inside the upper surfacearea of the insert. The protuberance 22 b preferably extends in adirection perpendicular to the central line L and is separated rearwardfrom the forward protrusion 21.

The radii of curvature of the convex curves of the protuberances 22 a inhemispherical shape and the protuberance 22 b in an elongatedhemi-cylindrical shape are preferably made large enough to enable asmooth surface contact to the inner wall 12 a of the central hole of theinsert.

The rear contact surface 25 of the rear protrusion 24 according to thepresent invention is convex curved in the vertical cross section passingthrough the central line so that the rear contact surface 25 comes intangential contact with a rearward slanting surface 41 of the toolholder 40, as can be seen in FIG. 1. It is even more preferable that therear contact surface 25 of the rear protrusion 24 is convex curved inthe transection cutting through the contact surface as well as in thevertical cross section passing through the central line, as can be seenin FIGS. 4 and 5.

On the other hand, an extension pin 26 is formed at the bottom end ofthe rear protrusion 24 and received in a recess 43 of the tool holder sothat the insert clamp 20 does not fall off from its own position evenwhen the clamping screw 20 is not firmly tightened.

The insert clamp according to the present invention has the followingtechnical effects.

Since a distal portion of the inside surface of the forward protrusionis provided with a protuberance 21 b of convex curved surface to come intangential contact with the inner wall of the insert, the insert clampaccording to the present invention has an effect to prevent wearing atthe contact point, which may occur in the prior art shown in FIG. 6,and, therefore, to provide a durable clamping. Also, by excluding pointcontacts with displaced contact either at a lower point (point “C”) or ahigher point (point “D”) as depicted in the prior art of FIG. 7, theinsert clamp of the present invention has an effect that a smoothsurface contact between the forward protrusion 21 and inner wall 12 a ofthe insert hole is guaranteed, while the point of action for thetransverse clamping force is stably fixed at the middle height of theinsert hole 12. This structure also allows a clearance between an upperrim 11 a of the insert hole 12 and a corner 21 c of the clamp bottomface so that the clamp 20 and the insert 10 may achieve a snug coupling.

Since the protuberances 22 a, 22 b on the bottom surface of the centralbody portion of the insert clamp has convex curved surfaces to come intangential contact with the upper surface of the insert, the clamp ofthe present invention has an effect to prevent displaced point contactseither at a forward position (point “A”) or a rearward position (point“B”) as depicted in the prior art of FIG. 6 so that a smooth surfacecontact is guaranteed at a fixed position. Especially, since the smoothsurface contact by the protuberances 22 a is located in rearwardseparation from the insert hole wall 12 a, an effective counterforce isprovided against the force lifting the rear portion of the insert apartfrom the bottom face of the insert pocket due to a shear force appliedon the insert nose. Also, since pressing down forces by tangentialcontact with the upper surface of the insert are applied on both regionsof the bottom surface of the central body portion which is bisected by acentral line passing through the forward protrusion 21 and the screwhole 23, although shear force is mainly applied on one active edge ofthe two edges adjacent to the nose, an effective counterforce isprovided against the tendency of lifting a portion of the insertopposite to the active edge apart from the bottom face of the insertpocket. This effect becomes more pronounced if the insert is intriangular shape for which there is only one upstanding support surfacein the insert pocket.

In one embodiment of the insert clamp according to the presentinvention, since the rear contact surface 25 of the rear protrusion 24is convex curved in the transection cutting through the contact surfaceas well as in the vertical cross section passing through the centralline, the rear contact surface 25 and the rearward slanting surface 41make a smooth surface contact at a certain position on the central line.Therefore, the rear contact surface 25 and the two protuberances 22 a onthe bottom face constitute a strong and stable support structure,so-called ‘triangular support structure.’ Especially, this ‘triangularsupport structure’ provides an effect to guarantee a stable and strongclamping state even for cases where two corresponding contact portionsare not symmetric with respect to the cross sectional plane of FIG. 1containing the central line and the two contact portions are ratherimbalanced in their heights.

Since this ‘triangular support structure’ is also constituted among theprotuberance 21 b of the forward protrusion 21 and the two protuberances22 a on the bottom face, the insert clamp 20 in accordance with thepresent invention has an effect to provide a durable and stable clampingstructure with no mobility over the entire body of the insert clamp.

The effect of ‘triangular support structure’ is also applicable for aninsert clamp having the protuberance 22 b in elongated hemi-cylindricalshape.

The present invention is applicable for the industrial field of cuttingtool holder assemblies.

The invention claimed is:
 1. An insert clamp for securing a cuttinginsert to a tool holder, the cutting insert having a central hole withits axis perpendicular to an upper surface, comprising: a forwardprotrusion to be received in the central hole of the insert, a centralbody portion provided with a pressing part to press down the uppersurface of the insert and a screw hole for a clamping screw to passthrough, and a rear protrusion having a rear contact surface to come incontact with a rearward slanting surface of the tool holder; wherein:the forward protrusion is formed on the forward end of the insert clamp,an inside surface of the forward protrusion extends downward in a spacedstate apart from the inner wall of the central hole of the insert, and adistal portion of the inside surface of the forward protrusion isprovided with a protuberance of convex curved surface to come intangential contact with the inner wall of the insert; and the pressingpart is formed on the bottom surface of the central body portion of theinsert clamp, and has convex curved surfaces to come in tangentialcontact with the upper surface of the insert on both regions of thebottom surface of the central body portion which is bisected by acentral line (L) passing through the forward protrusion and the screwhole.
 2. The insert clamp according to claim 1, wherein the pressingpart is a pair of protuberances in hemispherical shape separated by alength spanning across the central line (L) inside the upper surfacearea of the insert.
 3. The insert clamp according to claim 2, wherein aline joining the pair of protuberances is perpendicular to the centralline (L) and is separated rearward from the forward protrusion.
 4. Theinsert clamp according to claim 1, wherein the pressing part is aprotuberance in an elongated hemi-cylindrical shape extending across thecentral line (L) with a length spanning inside the upper surface area ofthe insert.
 5. The insert clamp according to claim 4, wherein theprotuberance extends in a direction perpendicular to the central line(L) and is separated rearward from the forward protrusion.
 6. The insertclamp according to claim 1, wherein: the rear contact surface of therear protrusion is convex curved in a transection cutting through thecontact surface as well as in the vertical cross section passing throughthe central line (L).
 7. The insert clamp according to claim 1, wherein:an outside distal portion of the forward protrusion is chamfered orrounded.
 8. A tool holder assembly comprising: a tool holder having aninsert receiving pocket; a cutting insert seated in the insert receivingpocket; and an insert clamp retaining the cutting insert in the insertreceiving pocket, wherein: the insert clamp is in accordance claim 1.